1. Field of the Invention
The invention relates to a weldment (or welded assembly) and a method of manufacturing the weldment.
2. Description of the Related Art
In industrial products such as electronic devices and vehicles, a copper wire is sometimes used under a harsh condition. In order to provide a copper wire endurable under the harsh condition, a dilute copper alloy material which can be manufactured by a continuous casting and rolling method, etc., and has an improved strength greater than that of pure copper while maintaining conductivity and elongation characteristics to a pure copper level has been being developed.
A dilute copper alloy material is demanded to be a soft conductor having a conductivity of not less than 98%, preferably not less than 102% as a general purpose soft copper wire or a soft copper material to which the softness is required. The intended purpose of such a soft conductor includes a cabling material for commercial solar cell, an enameled wire conductor for motor, a high-temperature application soft copper material used at from 200 to 700° C., a molten solder plating material not requiring annealing, a copper material excellent in thermal conductivity and a material alternative to high purity copper.
A raw material as the dilute copper alloy material is manufactured by basically using a technique of controlling oxygen in copper to not more than 10 mass ppm. It is expected to obtain a dilute copper alloy material having high productivity and excellent in conductivity, softening temperature and surface quality by adding a small amount of metal such as Ti into the base raw material so as to form a solid solution.
Regarding conventional softening, the result has been obtained in which the softening of a sample in which 4 to 28 mol ppm of Ti is added to electrolyte copper (not less than 99.996 mass %) occurs earlier than a sample without addition thereof (see, e.g., “Iron and Copper” by Hisashi Suzuki and Mikihiro Sugano (1984), No. 15, 1977-1983). According to “Iron and Copper”, a decrease of sulfur incorporated into a solid solution due to formation of Ti sulfide causes softening to occur in early stage.
Meanwhile, it has been proposed to continuously cast in a continuous casting apparatus using a dilute alloy in which a small amount of Ti is added to oxygen-free copper (see, e.g., JP patent Nos. 3050554, 2737954 and 2737965). Furthermore, a method of reducing oxygen concentration by a continuous casting and rolling method has been also proposed (see, e.g., JP patent Nos. 3552043 and 3651386). In addition, it has been proposed that, when a copper material is manufactured directly from molten metal of copper by the continuous casting and rolling method, the softening temperature is lowered by adding a small amount of metal such as Ti, Zr or V (0.0007 to 0.005 mass %) to the molten metal of copper with an oxygen amount of not more than 0.005 mass % (see, e.g., JP-A-2006-274384). In this regard, however, the conductivity is not examined in JP-A-2006-274384 and the manufacturing conditions for achieving both of the conductivity and the softening temperature are unknown.
On the other hand, a method of manufacturing an oxygen-free copper material having a low softening temperature and high conductivity has been proposed. That is, a method has been proposed in which a copper material is manufactured by a drawing-up continuous casting apparatus using molten metal of copper in which a small amount of metal such as Ti, Zr or V (0.0007 to 0.005 mass %) is added to the oxygen-free copper with an oxygen amount of 0.0001 mass % (see, e.g., JP-A-2008-255417).
Meanwhile, TIG (Tungsten Inert Gas) welding is a technique for fusion-welding a copper material. Only high purity copper and oxygen-free copper with a low oxygen concentration of less than 2 mass ppm are the materials which allow this welding method to be used.